There are code issues here as you know by what you're inquiring about. I suggest you contact the sewer folks 'bout this because they have all the answers you need. IN fact, if you find this job to be more than you want (which I say it is), perhaps they can recommed 2 or 3 companies that install the pipe. I've been going to my Township's Sewer Authority meetings for about 2 years now and no one has ever come in to ask to do this job. I can't believe you're willing to do this unless you have the equipment. Depending on the depth of your lot, you may have your work cut out for you.
Now, it isn't completely out of the ordinary to want to save some $$$ on this type of work. However, if you have a contractor do this, you may be able to see if you can save some $$$ by doing the digging yourself; not the pipe work. The contractor (if they're willing) will tell you the depth and width of the trench. Perhaps you need a gravel bed too before the pipe is layed. And lastly and probably most importantly, you need to have a 'company' come out and mark your telephone, cable, gas, electric, water, etc., etc., lines so they don't get damaged when digging. If you find out that ANY of the utility lines are near where you're working, and if YOU damage them, you're responsible! This is when I'd say you're in over yer head.
I wish I had better news for ya. My best to ya and hope this helps. PS: In Pennsylvania, there's a company called Pennsylvania One that will come out to the home for free to mark the utility lines. If you call any of the utility companies, they'll be able to give you the proper contact for the similiar company in your state. It's a free service here. There were here in 2 or 3 days after I called. Please understand, each of the utilities buries their utility at different depths. Anywhere from 3" to 3' so it's not that straight forward. Just where you think (or don't think) there's a utility, BOOM! Also, this company should give you a pamphlet on how to 'read' their markings (whether you do the work or not). Get it! And, for future reference, take pictures of the marking BEFORE you dig in case you have a problem and want to seek recourse.